To increase the power of an internal combustion engine, use is made of exhaust-gas turbochargers which have a compressor positioned upstream of the engine and have a turbine, connected via a common shaft, in the exhaust tract of the internal combustion engine. The supercharging of an internal combustion engine increases the air flow rate and thus also the fuel flow rate into the cylinders, resulting in a significant increase in power of the engine. The exhaust-gas turbochargers used for this purpose are, as standard, made up of a rotor including compressor wheel, turbine wheel and shaft, and of the shaft bearing arrangement, the flow-guiding housing parts (compressor housing and turbine housing respectively) and the bearing housing.
Known internal combustion engines can be supercharged by means of exhaust-gas turbochargers in single-stage combination with one turbocharger per engine bank resulting in pressure ratios of up to PIV=6. One possible system diagram of the single-stage supercharging configuration is shown in FIG. 3. For the newer generation of internal combustion engines, the pressure ratio is being increased, by means of two-stage supercharging, to up to PIV=12 and greater. The benefit of two-stage supercharging lies substantially in a considerable reduction in NOx exhaust-gas emissions, an increase in engine power density, and in an increase in engine efficiency.
The two-stage supercharging system is made up primarily of a series-connected low-pressure and high-pressure turbocharger and of an additional intercooler between the two compressor stages. One possible system diagram of the two-stage supercharging configuration is illustrated in FIG. 2 alongside the system diagram of the single-stage supercharging configuration. Owing to the intercooling, less compressor work is specified for the compression of a predefined air flow rate and pressure ratio, whereby the efficiency of the supercharging system can be increased. Finally, analogously to the single-stage system, the compressed air from the two-stage supercharging system is cooled by the charge-air cooler at the inlet of the internal combustion engine and is conducted into the engine.
By comparison to the single-stage system, the structural volume to be attached to an internal combustion engine in the case of a two-stage supercharging system is, with the additional components, significantly more complex and of greater inherent volume. Through logical integration of the specified components, however, said structural volume can be reduced, and the supercharging system made more compact.
With a two-stage supercharging system, the number of turbochargers and cooler assemblies specified for an internal combustion engine is doubled in relation to the single-stage system, whereby the complexity of the line guidance and the size of the structure to be attached to the engine increase. For example, the connecting lines between the compressor stages and the intercooler and the additional exhaust line between the high-pressure turbine stage and the low-pressure turbine stage should be integrated in the structure to be attached.
The attachment concept and the line guidance are highly dependent on the respective type of construction of the engine, because the exhaust lines are in part guided to the side of the engine or centrally with respect to the engine axis. The position of the fresh-air lines is likewise dependent on the type of construction of the engine. FIG. 1 schematically shows attachment options of exhaust lines (E) and fresh-air supply lines (A) for V-configuration engines according to an exemplary embodiment of the disclosure. The attachment situation in the case of in-line engines with only one engine bank corresponds to one half of the attachment situation in the case of a V-configuration engine.
The high-pressure and low-pressure chargers should be located on the engine such that the exhaust lines and fresh-air supply lines between the supercharging system and the engine and between the supercharging system and the cooler assemblies have the minimum possible structural lengths and structural volumes. It should also be ensured that the flow guidance in the lines exhibits the fewest possible diversions for the benefit of low flow losses.